Add regress test from Ayman Bagabas.

regress/tab-cell-background.sh

@@ -0,0 +1,43 @@
+#!/bin/sh
+
+# When a write breaks up a wide character or a tab, the columns it covered must
+# keep the background colour, both in the grid and on the terminal. The second
+# server is attached to the first so that what is actually sent is checked, not
+# just what tmux has stored.
+
+PATH=/bin:/usr/bin
+TERM=screen
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+$TMUX kill-server 2>/dev/null
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+$TMUX2 kill-server 2>/dev/null
+
+TMP=$(mktemp)
+trap "rm -f $TMP" 0 1 15
+
+# 1. Write inside a tab. 2. Overwrite the right half of a wide character.
+# 3. Two tabs of different colours, the first partly deleted so that padding
+#    from both ends up next to each other, then written over.
+# The sleep is so that the client is attached before anything is written and
+# the changes are sent as they happen rather than as one redraw.
+$TMUX2 -f/dev/null new -d -x24 -y3 "
+	sleep 2
+	printf '\033[44m\033[K\t\033[4GX'
+	printf '\033[2;1H\033[44m\033[K\344\270\226\033[2GX'
+	printf '\033[3;1H\033[42m\033[K\t\033[43m\033[K\t\033[0m\033[4G\033[8P\rx'
+	cat" || exit 1
+$TMUX2 set -g status off || exit 1
+
+$TMUX -f/dev/null new -x24 -y4 -d "$TMUX2 attach" || exit 1
+sleep 4
+
+$TMUX capturep -pe -S0 -E2 >$TMP || exit 1
+$TMUX kill-server 2>/dev/null
+$TMUX2 kill-server 2>/dev/null
+
+printf '\033[44m   X\n X\n\033[49mx\033[42m  \033[43m             \033[49m\n' |
+	cmp - $TMP || exit 1
+
+exit 0